Good News & Best Laid Plans

It's now mid-February and two important things have happened:

• We've received our first full-month Rocky Mountain Power (RMP) utility bill since the installation of our PV system went on-line, and
• Tigo has sent the latest version of their MMU & LMUs for replacement on the solar modules.

Our RMP bill was half of what it was a year ago!

Granted, weather conditions have a dramatic affect on power usage, but this type of reduction is a very hopeful sign.

As mentioned in an earlier posting, Tigo had offered to send out the "latest version" of their MMU and LMUs for a wholesale replacement of those which I'd installed in December. I took them up on this offer in that the earlier equipment was some of the first to come off of their new production line and the effort required to get it all working properly would certainly be greater than just replacing everything. Plus, the latest version of their LMUs promised better efficiencies in power production.

Now to schedule a day when my co-installer (my son) and I could perform the swap. It had to be a Saturday since my son was out-of-town every week for five weeks. We picked a week in February and set our plans.

Three days before our planned re-installation: The weather looks like it will be great with clear skies and temperatures in the 40°Fs.

Two days before our planned re-installation: The weather is starting to look iffy but perhaps it will still prove acceptable. I also prepped everything by pulling the new equipment out of the boxes and getting it staged for rapid assembly once the swap-out started. It was fortunate I did the prep because I discovered that the new LMUs mounted with pressure clips instead of screw clamps AND THERE WERE NO CLIPS INCLUDED IN THE SHIPMENT!

A quick call to Tigo and a bunch of clips were shipped overnight. What a great bunch of guys! No, "Well, I'll have to get back to you on that." Just a, "I'm so sorry! You'll have them tomorrow."

One day before our planned re-installation: The weather is clearly deteriorating and it looks like we're going to have to put things off.

The day of the planned re-installation: Rain! No way I'm getting up on the roof in rain!

Meanwhile, the existing setup (i.e. without the Tigo system fully operational) was producing lovely amounts of electricity, especially on sunny days.

Shocking Developments

An exciting day!

Rocky Mountain Power arrived in just a couple of days of my request and performed the meter swap. I was so excited that I forgot to take pictures.

The technician was very careful. The safety considerations were obviously important. He wore heavy gloves and a full face shield. Where previously he would have just broken the meter seal and yanked the old meter off by hand, he now employed a very heavy duty plastic tube-like device which surrounds the meter and clamps on, and, after a slight tug, removes the old meter. The new meter is installed using the same tool.

He explained that they do this now because so many meters have exploded because of some short that occurs when removing or installing the meter.

Of course, I'm just standing there watching with no face shield or other protective gear.

The longest part of this process was spent in the RMP truck programming the new 'smart' meter.

The new meter, among other things, records a) power sucked from the utility (consumed), and b) power pushed to the utility (produced). Our new power bill will show these two numbers, calculate the difference, and bill us for that difference.

So, if in a month we consume 70 kWh and produce 50 kWh then we will have to pay for 20 kWh. If we produce more in a month than we consume then it gets 'banked' for the next month. Anything still banked at the end of March of each year simply disappears. Since our intention was to minimize peak usage we are unlikely to have anything banked at the end of March.

The new meter also has an animated display and shows the two important numbers. If you look closely at the area highlighted in yellow you'll see a bar with an arrow pointing to the left. That's a good sign! It means our solar modules are producing more electricity than we are consuming and that the extra is being fed back into the utility. The bar animates and the faster it runs the more power is feeding in whatever direction.

Failure to Communicate

Meanwhile, it's back to figuring out why I'm 1) not seeing power being reported at the Tigo web site, and 2) not seeing any power at the inverter DC input.

Let's just make a long story less long.

December

We were never able to exactly identify the reason why the Tigo MMU/gateway was unable to communicate with the LMUs on each of the solar modules. I did discover that powering down the MMU would cause DC to appear at the inverter. This was somewhat of a surprise to me in that the individual LMUs moderate the voltage coming from the solar module to which it is attached and I had expected that failure to communicate would result in zero VDC. Tigo explained that the LMUs fall-back to just passing through the unmodified voltage in the case of a communication failure; makes perfect sense.

January

Once again I checked the continuity of the cable which runs between the MMU and the gateway. With Tigo's help I also checked the voltage inside the gateway and inspected the LEDs. Tigo sent out a new gateway. No change. Tigo sent out a new gateway cable. No change. Remember, this is all bleeding edge equipment so challenges like this were expected. In no way was I frustrated by these communication issues—the only anxiety I felt was that we could in fact get the Tigo Maximizers working.

February

So Tigo sent out replacements for everything: new MMU, new gateway, and 24 new LMUs!

I hate to keep you in suspense, but since this was still Winter and I despise working in sub-freezing weather I postponed getting back up on the roof until the daytime temperatures were going to be at least in the upper 40°F range.

Dotting the T's with Rocky Mountain Power

Now that the panels have been mounted, the inverter installed, conduit run, disconnect installed, and the DC and AC wiring completed it's time to get Draper City to send out their building inspector for a final electrical inspection and Rocky Mountain Power (RMP) out to swap the meter and get this system producing!

Draper City is very responsive and an inspection was scheduled for the next day. The inspection was mostly chewing the fat about solar, how it's an 'emerging' technology, how nice the panels look and what the pay-back was expected to be. If Vince and I hadn't opened up the main service panel and opened the cover of the AC disconnect I don't think they would have gotten a look-see. Sorta reminded me of a guided tour.

I had previously (that is, months ago) completed and mailed in to Rocky Mountain Power the Interconnection Agreement for Utah. I'd called in to verify that they had received it and was instructed to call back when the system was ready for inspection. So I made the call and asked for an inspection. Before RMP could inspect and do the meter-swap they required a copy of the city building inspector's report to be mailed in—and they apologized for not following-up by sending me the packet of information which would have given me detailed instructions on what to do as the power-up day approached. Also, a separate inspection visit by RMP would not be required if I provided photographs showing that the 'signage' at the main service panel met their requirements.

Rocky Mountain Power has an office only a couple of miles away so it was easy to run over a copy of the city inspection approval and photos of the signage. Everyone there pretty much wears heavy work boots and wears suspenders. They promised to get the installer scheduled within the next two weeks Since net-metering is an 'emerging' technology they warned me that a meter might have to be ordered and that only properly trained technicians could perform the install. This kind of talk made me nervous since I needed to have the system functional before the end of the year to guarantee that we could take the federal tax credit for 2009—who knows what might happen to that credit if it slips a year! I mentioned this concern to them and subtly reminded them it was they who'd jeopardized the schedule by not sending out the preparatory material.

One more trip was made to the RMP office to drop off the completed and signed the net metering agreement, the one they had neglected to send as part of the preparatory material.

Oh, and one other thing: we notified our home owners insurance carrier that we had installed the solar equipment and made sure our coverage was increased as needed.

Catching Up: Inverter & Wiring Installation

The Tigo folks, in particular Daniel and Stuart, have gone above and beyond in helping to figure out why there did not seem to be any communication between the MMU and the gateway. We spent a bit of time on the phone with the cover off of the gateway box, prodding and poking and looking at LEDs to see if we could figure out what might be wrong.

Meanwhile, Vince Landvatter and his brother, both master electricians, came by and we got the inverter mounted, the high-voltage DC wiring run, the AC feed to the service panel installed, the AC disconnect mounted, and the heavy-duty Tigo MMU box set up.

The inverter, a Fronius IG Plus 5.0, is mounted inside our garage, thus keeping it out of the elements and in a more moderate climate. Our outdoor temperatures range from just above 0°F to 110°F over the year. Also, the most convenient locations outdoors would be in full sun, which is something I wanted to avoid. This indoor location is just around the corner from the service panel.

Once the electricians got the Fronius mounted, I popped it open (the bottom part that is), pulled off the cover panel, removed the insulating sheets, and pulled the slugs Fronius had pre-installed in the fuse holders. DON'T FORGET TO DO THIS BEFORE THE DC FEEDS FROM THE MODULE SERIES ARE HOOKED UP!

The outdoor installation includes the main service panel, the AC disconnect, a place for the Tigo MMU, and, very importantly, signage.

The small box in the middle is the AC disconnect. It must be located very near (i.e. adjacent to) the main service panel so that a utility technician can pull the disconnect should maintenance work be required in the area. In this case, the AC disconnect is redundant (but required by the utility for safety) since the Fronius will automatically shut down the AC feed should it discover no AC on the utility side of things.

The beige box in the right is where the Tigo MMU goes. The flexible conduit coming out of the bottom of that box and snaking upwards is for the gateway cable. The flexible conduit coming out of the bottom of the Tigo box and snaking to the left is for the ethernet cable.

The beige box just below the AC disconnect is the network interface box. Formerly used by the telephone company, I had the foresight when building the house to pull four Cat 5e ethernet cables from the utility room. This was very convenient for use by the Tigo MMU to connect to the Internet and Tigo's monitoring web site.

The electricians got everything wired up so all we need now is for Rocky Mountain Power to come and inspect things. Well, almost ready...

One last thing to do: check the module series voltages at the inverter. And it's a good thing I did! And it's a good thing I pulled the fuse slugs earlier! Because one of the module series had been wired in reverse. A quick trip to the j-box on the roof and everything was back on track.

Catching Up: Mid-December

First, let me apologize for not updating my blog for several months. Life is busy and while the path may have been a bit rocky, the ultimate outcome of this project has been very satisfying.

When we last left the story, the day was too long in the tooth to do any MMU/LMU testing. The next morning, after sunrise, I was back outside with my handy Fluke 12 Multimeter checking the string voltages. All three strings were reporting full voltage of around 385 VDC! I decided to keep an eye on things and move ahead with getting the Tigo MMU up and running. Doing so would allow me to monitor each individual panel performance on the Tigo web site.

The MMU connects to the Internet in order to send data to Tigo's data center. There is a 'gateway' box connected to the MMU. This gateway communicates with the LMUs wirelessly. It allows the MMU to collect performance data and to control the power output of each module.

The Tigo gateway is connected directly to the MMU by a small, four conductor cable. The cable is quite long and allows great flexibility in the placement of the gateway, which I was to learn later was very important.

Here's how it all fits together, communication-wise:

I temporarily installed the MMU in our laundry room, which is just through the wall from our main electrical service panel and with a convenient ethernet nearby. I placed the gateway in the window with the face of the gateway aiming towards the array, connected the ethernet cable, and plugged in the power.

Things are looking good: The MMU 'boots' up. I play with the simple menu system and discover the IP address and see that it's connected to the Internet. Then it's a quick trip to the Tigo web page showing my system and...

...everything is gray. No information coming from the LMUs! Hmmm.

In the meantime, the electricians have a job to do in Deer Valley and I must wait a couple of days before they can come and get the inverter mounted, the high-voltage DC wiring run to the inverter, the AC feed to the main service panel, the outside AC disconnect installed, and various other odds and ends.

Panel Installation, Part 2

The Next Morning

Early the next morning we were off to Nuts & Bolts Supply who could supply us with the proper stainless hardware, then back home to replace those 42 mid-clips and bolts which, as you have guessed by now, required sliding everything off, replacing the bolts, and sliding everything back on. The new wrinkle this time was that over the night moisture had condensed on the rails, in the track, and had frozen. It took some effort to get the old bolts off.

Things started to move pretty smoothly. A neighbor had very kindly loaned us a scissor lift which made the job oh so much easier.  Once we got the first nine panels in place we tested the 'A' string with a voltmeter. The meter read a very pleasing 387 VDC!

Note that it is very important to use a proper torque wrench when tightening the end-clip and mid-clip bolts. Exceeding the recommended torque will easily damage the panels by cracking the tempered glass. It's also critical to avoid damage the back of the panels since it consists of a thin coating over the back of the individual cells and scratching of that coating would be a serious matter.

As each string of 8 panels was completed we tested the output voltage to make sure we were getting the desired output. We finished mounting the panels just as the sun set (and things started to get really cold) and it was not possible to test the final string since there was no longer adequate light.

Putting that last panel up was very satisfying. I tried to give my son a hug, he went on his way, and I cleaned up all of the cardboard from the panels while collecting the serial number stickers for my records.

The next morning, after the sun came up, I went out and measured the voltage of the final 'C' string and double-checked the 'B' and 'A' strings.  'C' and 'A' was fine but 'B' was measuring only 334 VDC, indicating that one panel was not producing. Since I was getting some voltage I concluded that the Tigo Maximizers were properly wired to one another. The problem had to be either a bad connection between one panel's output into its Tigo Maximizer or a Maximizer was flaky.

The best way to identify the problem was by using the Tigo MMU (Maximizer Management Unit). Tigo had already set up my account at their web site so that once I hooked up the MMU to my Internet service I could go to that web site and see how each panel was performing.

There was some confusion on my part, mostly due to inadequate documentation of the MMU and how the Tigo products worked — but this was a brand new product and I had expected some 'bleeding' edge experiences along the way.

The installation manual for the MMU did not explain how to hook up the sensor/gateway cable. The sensor/gateway is a small box that wirelessly communicates with the 24 Tigo Maximizers (LMUs) which we had earlier mounted to the back of each solar module. I dashed off an email to James Bickford at Tigo and very quickly had a Tigo engineer on the phone helping me get things set up.  The engineer also explained that it was not necessary for the solar modules to be connected to an inverter in order to determine how each module was performing.

After some initial miscommunication, I got the sensor/gateway all cabled up, the MMU connected to the home's ethernet, and powered up. By this time the sun was going down and it was futile to see if there was any output coming form the panels.